A typical construction for both V- and I-type engines comprises a metal oil pan that is attached to the block so that the two cooperate to form the bottom of an engine crankcase that includes an oil sump. The oil pan has an upper perimeter rim that bounds an interior of the oil pan, and it is via that rim that the pan is attached to the block. A sealing gasket is disposed between the oil pan rim and a surface of the block to seal the joint between them.
In certain engines, clamps are used for the attachment of the oil pan to the block. A typical clamp is fastened to the block by a screw and is shaped to engage the rim of the pan so that as the screw is being tightened into the block, the rim is forced toward the block, compressing the gasket in the process. In order to protect the metal of the oil pan from corrosion, the pan is typically coated with a rust preventive.
The inventor has observed occurrences of fretting of the oil pan at the pan/block interface in certain engines that use clamps for attaching the pan to the block at various locations around the rim of the oil pan. Such occurrences can lead to premature failure of the interface that leads to oil leaking from the crankcase at the interface. The inventor has also observed that the onset of an incipient fretting failure is caused by the clamp wearing through the rust-preventive coating at a location where the clamp engages the pan rim and exposing bare metal of the pan to corrosion. As corrosion accelerates, a fretting fatigue crack or excessive oil pan material loss allows an oil leak to develop.